Optical instrument



NOV. 8, 1938. J REICHERT 2,135,531

OPTICAL INSTRUMEN? Filed Jan. 12, 1935 4 Sheets-Sheet 1 1a A INVENTOR. 3 15.5

. ARober? flnfezcherf ATTORNEY.

4 Sheets-Sheet 2 INVENTOR.

JKei ch er? ATTORNEY.

Nov. 8, 1938. R. J. REICHERT OPTICAL INSTRUMENT Filed Jan. 12, 1935 globerl' NOV. 8, 1938. RElcHERT 2,135,531

OPTICAL INSTRUMENT Filed Jan. 12, 1935 4 S heets-Sheet 3 E F I I 1 51 721% INVENTOR.

AK oberl'g. $92 chem?" BY ATTORNEY.

OPTICAL INSTRUMENT Filed Jan. 12, 1955 4 Sheets-Sheet 4 INVENTOR. flioberl' yflfliei cherl BY ATTORNEY.

Patented Nov. 8, 1938 UNITED STATES PATENT OFFICE 2 Claims.

My invention relates to optical instruments and more particularly to the type which'employs a system of lenses which invert the image, and in which it is therefore necessary to employ an in- 5 verting system to erect the image, and more particularly to an inverting system which employs reflecting surfaces.

Instruments for magnifying objects at a distance can be divided into two main groups, viz: those using a positive lens system together with a negative lens system (producing a virtual image) known as the Galilean system and those using two positive systems of lenses producing a real inverted image. With the latter system it is necessary to use some optical method of inverting this image so that it may be viewed in erect position. It is with this latter type of instrument that this invention is concerned.

There are two systems of inverting this image that have heretofore been employed; one by a system of two positive lenses placed in the optical axis. of course, elongates the instrument and is, therefore, only used in such instruments as terrestrial telescopes, etc., where length is not objectionable.

. The other system is to use a prism placed so as to invert the image. Various systems have been used, of which the most common is the Porro system. This consists of two right angle equilateral prisms having their hypotenuse faces parallel and their apices on opposite sides of the common hypotenuse plane. The apex lines of the prisms are at right angles to each other. In this system the light travels as 35 shown in Figure 2 (to be described in detail hereafter) from which it will be seen that'\the axial beam passes through the hypotenuse faces at right angles and is almost totaily reflected by the sides of the prisms.

In a binocular instrument it is" vital important that light originating from a sihgle point sourcejemerge from both sides of the binocular instrument as beams parallel to each other, so that when viewed by the two eyes they will give the impression of a single point, i. e. that they will'strike the retlnae of the respective eyes in conjugate points.

It has been impossible to design and build an instrument accurately enough to produce this parallelism, or rather to'keep' the divergence less than three minutes of arc which is the limit of the accommodation possible for the average eye. Greater divergence will cause a double image. Therefore, some means mus be provided to ad-v just the instrument during or after assembly.

prism, system ,or

If the two halves of the binocular are attached to each other by a hinge to allow adjustment of the distance between the eye-pieces, it is necessary, in order to have the parallelism for all interpupillary adjustments, to have the optical 5 axes on each side not only parallel to each other but also to the mechanical axis of the hinge. Heretofore such adjustments have been achieved by moving the prisms individually in a direction perpendicular to the axis of the optical path and parallel to the hypotenuse; by rotating the objective lenses which are mounted eccentrically or by moving one side of the binocular instrument. as a whole relative to the mechanical axis of the binocular.

These methods, however, are unsatisfactory owing to the small space available for such adjusting mechanisms, especially when such mechanisms'are extended through the wall of the instrument in order to allow such adjustments to be made after the instrument has been assembled.

Moreover those systems in which the prisms are moved individually are unsatisfactory in that the prisms are not rigidly enough held in position to withstand the rough usage to which most optical instruments of this type are subjected.

I have discovered that I can obtain the desired rigidity of the prisms or other reflecting surfaces while obtaining adjustments thereof by rigidly mounting the reflecting members in a central housing and performing the necessary adjustments on the central housing.

Accordingly, objects of my invention are: to provide a novel adjustment means for displacing the outgoing beam of the erecting system with respect to the incoming beam; to provide a novel supporting means and adjusting means for said support of the reflecting surfaces; to provide a novel support for said reflecting surfaces (to be known hereafter as the central housing) to provide a novel adjustment of said central housing in a housing (to be known hereafter as the main housing) of the instrument, to provide a novel means of mounting the reflecting surfaces in a central housing so that all these reflecting sur- 45 faces retain a; fixed relative position to each other and to the central housing, to provide novel means for adjustment by one of the following or combination of any or all:

1. A lateral adjustment in the hypotenuse plane, the reflecting surfaces remaining parallel to their original position.

2. Rotation about an axis or axes perpendicular to the hypotenuse plane.

central housing is held rigid by being attached a at one point to the main housing by means of a semi-rigid screw and also by means of two screws rigidly attached to the central housing and said screws held under tension by screw heads held in place in the main housing.

Heretofore, prisms have been used in practice for providing the necessary reflecting surfaces to the practical exclusion of ore due to the fact that rear surface reflecting mirrors produce a double image owing to partial reflection onthe front surface. Attempts to use front surface metal reflecting mirrors such asstainless steel have been optically unsatisfactory. It has also been proposed to use plating on metal but this is unsatisfactory owing to the impossibility of obtaining an optically plane surface on the metal base.

I' have discovered that I can materially increase the percentage of .light transmitted by the inverting system by replacing prisms by a glass surface covered with a suitable metal or metallic substance which produces a good optical reflecting surface when made in a special manner.

Accordingly, objects of myinvention are: toprovide, in an inverting system as defined in paragraph one of this application, means for increasing the percentage of light transmitted by the inverting system. to provide a novel re- I fleeting medium; to provide a novel reflecting surface; to provide a novel reflecting surface on the outer face of glass; to provide a novel reflectin surface produced by the cathode sputtering process of aluminum or other metallic substance.

There are other objects of my invention which together with the above'will appear in the detailed descriptions which follow in connectionwith the drawings in which e 1 is a standard diagram of the light rays of an optical system using two positive lens systems and producing an inverted image.

Figure 2 is a perspective of a prism system known as the Form system.

Figure 3 is a light diagram illustrating the partial erection of an image by the first prism of Form erecting system. 1 I

Figure 3A is a light diagram illustrating the Figure 7 isa cross-sectionthru 1-4 of Figure 6.

Figure 8 is a partial elevation and cross-section showing my optical system with my novel adjustment for the central housing.

Figure 9 is a partial elevation and cross-section thru 9-9 of Figure 8.

' Figure 10 is a detail of an alternative adiust surface sho my novel reflecting system of mirrors and my novel adjustment for the central housing in which the mirrors are rigidly mounted, and

Figure 14 is a perspective of my novel mirror system.

Referring to Figure 1, a cemented doublet i and 2 forms one of the positive systems. A cemented doublet t and E and a planoconvex lens 3 form the other positive system. As shown by the rays a, b and 0 coming from a point at in= finity and going thru this complete system, the image is inverted. K

These lenses are mounted in a suitable main housing so that therays of light which pass t the system are reflected at plane surfaces, in such a manner as to erect the image. Such a system consisting of two rectangular right angle lateral prisms d and l is shown in Figure Prism 6 comprises a hypotenuse face s-sid-ii; two reflecting faces t--ii-i2it and 9-i@-i2--ie and line 82-i3 is the apex. Prism l comprises a hypotenuse face lii s-usii and two reflecting faces iii-id-iQ-ifl and i5ii-i8i and line iii-ls is the apex. These two prisms are placed so that the two hypotenuse faces 8-9-lt-H and iii-it-iti? are parallel; the spices 52-53 and it-it are on opposite sides of the hypotenuse faces and the lines of the apices iii-83 and it-it are at right angles to each other:

These prisms are'so mounted in the central housing that incident'light as illustrated by rays A and B enters the prism system thru half of the hypotenuse face 3-9-49-86 at approately right angles thereto and strikes the surface 8-'-& i-i 2 9 3 where most of it is reflected to surface 9--i@i2-i8 where most of it is again mflected and leaves prism t thru the other half of the hypotenuse surface, 8-t-it-i i. The light then enters prism 1 thru half of the hypotenuse face lfl-de-id-il, and strikes the reflecting leaves theerectlng system thru the other half of' the hypotenuse face it-id-it-fl.

In Figure 3, O is an image formed by the objective i and 2 as shown in e 1. Figure 3 shows that after reflection in surface 8l l-ifii3 OPQR takes the position OrPrQrRi. After reflection in surface 9iu-=i2--i3 the ge takes the position 02P2Q2Rz. view of the image QzRs. after reflection in surface itl5-i9i8, and the side view of the image after reflection in l6li--l8-i8. The flnal image O4P4Q4R4 is shown in me 3 from which it will A shows a side,

is the side view surface as-ts-as-rs where most of it is rebe seen thatthe image 0R has been totally inverted by the four reflections.

These prisms are rigidly mounted on a plate or housing to be hereafter called the central housing.

They will then retain their relative position -.throughout any movement of the said central housing. Such a central. housing is shown in Figure 4 and Figure 5. v

In Figures 4 and 5 the main plate which the respective hypotenuse faces of the prisms B and i rest; one prism being onone side, of the plate and the other'prlsmbeing on the other side of the plate.- J j Four pillars 23 are rigidlyfastened to the plate at right angles forming an integral. part of the central'housing and extend on either side of the prisms t, and l. Across the top ofeach pair of or central housing has indentations 22 on bothsides in pillars 23 are fastened springs 24 pressing on the apices of the prisms B and and hold the prisms rigidly in the indentations 22 in the central housing. Suitable openings 25, 26 and 21 are made in the central housing to allow for the passage of the light rays.

Any other system of prisms which will invert the image can be used such as any of the systems described by specifications given in Application of the Algebraic Equations to Optical Design #550 vol. 22 of the Scientific Papers of the Bureau of Standards, pp. 176, 1'77, 178, 1'79, 180, 182 and 183 whether with the exact specifications mentioned or other suitable ones.

A novel system which I discovered is shown in Figure 14. Two mirrors 40 and 4| defined by points 2829-303| and 303|32-33 are made from pieces of rectangularly shaped optically plane glass having one surface covered or plated with aluminum metal particles by the cathode sputtering process. One such process comprises placing the mirror to be coated under a bell jar of glass. Some inches beneath it, there is a coil of wire in which is placed a small scrap of aluminum. The bell jar is sealed and the air pumped out to a very low vacuum, then the coils are heated electrically which evaporates the metal and it recondenses on the glass.

Air is then admitted and converts the top layer of the aluminum into aluminum oxide known as alumina, which acts as a non-corrosive and nonoxidizable protection. 7

It is believed that the sputtering process consists of covering the surface with an atomic layer of metal.

In accordance with this process, a mirror surface is formed on the optically plane glass which will reflect light to the degree ofperfection required and will not tarnish when exposed to the air. Such a reflecting surface is far superior to prisms in that the absorption of light by the four mirrors is approximately 5% as against 30% for the prisms. It will be obvious that other sputtering processes of applying aluminum or other metals to glass may be employed. In this sputtering process the metal coating is believed to be held in contact with the glass base by atomic cohesion and thus produces a reflecting surface, as plane as that of the base.

These mirrors are mounted with their covered or mirrored surfaces towards each other, having a common side 30-3l and having their surfaces at right angles to each other.

Two similar mirrors 42 and 43 defined by points 3435363'| and 363'|38--39 are similarly mounted. The four mirrors are mounted in the central housing as shown in Figure 6 in such a manner that, line 303| is a perpendicular to line 3631 and the plane formed by points 2829-3233 is parallel to the plane formed by points 34-35-38-39.

Light entering this system represented by C and D in Figure 14 will first strike mirror 40 and be reflected on to mirror 4| where it will be again reflectedto mirrorfl andagain reflected on tg mirror 43 after which it will emerge as rays par-' allel to the rays entering the system. Moreover the image after reflection in the four mirrors will have been completely inverted.

One method of mounting the mirrors rigidly in the central housing is shown in Figure 7. The mirror 43 is placed in an indentation 44 formed in central housing. Suitable openings are provided in the central housing to allow for the passage of the light rays. Cement or glue is used to hold the mirror rigidly in the indentation 44.

Any other system of mirrors or any combinattion of mirrors and prisms which will erect the image can be used.

The lenses I, 2, 3, 4 and 5 together with the central housing are mounted in a suitable housing as shown in Figures 4, 8 and 13. Lenses 3, 4 and 5 are mounted in a standard eye-piece housing to which is attached a standard eye-cap. Lenses and 2 are mounted in a standard objective housing.

In Figure 4 which shows a monocular, the central housing is held rigidly in the main housing by means of screws 45.

Figures 8 and 9 and 13 show a binocular design embodying my novel method for adjusting the central housing and for holding the same rigid after adjustment has been made. A screw 46 holds the central housing to the main housing of the binocular. It is of sufficient elasticity to allow for any slight rotation of the plate 20 acting as a universal joint; A 4--4|J brass screw fulfills this condition.

Long screws 41 and 48 as shown in Figures 8, 9

and 10 are made integral with or rigidly attached to the central housing 20. These screws extend to either side of the central housing, their ends being threaded. Opposite the ends of these screws are openings in the main housing in which screw-heads 49 are fitted. These screw-heads 49 are internally threaded to receive the threaded ends of screws of 41 and 43.

' Thus by tightening the screw head at one end of screw 41 and loosening the screw head at the opposite end, the central housing will be rotated about an axis thru screw 46 and perpendicular to screw 48. Similarly by a tightening and loosening of the screw heads on screw 48, the central housing can be rotated around an axis thru screw 46 perpendicular to screw 41. After the adjustment has been made, the screw heads can be tightened and the central housing will then be held rigidly in placarelative to the main housing, especially as the screws 41 and 48 will then be under tension. If owing to the construction of the instrument it is not feasible to extend either or both screws 41 and 48 in both directions to reach the screw heads extending thru the main housing, it is satisfactory to divide either or both screws into two parts, as shown in Figure 10 where the two screws 50 and 5| take the place of the single screw 41 or 48. However, if a plane perpendicular to screws 50 and 5| thru screw 45' meets screws 50 and 5| in E and F, the points 46, E and F should liein an approximately straight line.

As explained previously, it is necessaryin a binocular construction to provide an adjustment which will, by moving the optical axis of the light passing thru the erecting system, bring the images of both sides of the binocular intocoincidence for all interpupillary distances. I have discovered that this can be done by a lateral movement of the central housing in a plane parallel to the two apices l2-l3 and |8--|9 of the prisms or parallel to the'two common sides of the mirrors viz -3| and 3|. Such a plane is shown in Figures 11 and 12. AB is the plane of the normals to the reflecting surface of the first prism or to the first two mirrors and 4|. BC is the similar plane of the normals to the reflecting surfaces of the second prism or to the normals to the second pair of mirrors 42 and 43. An entrant ray meets the plane of the paper in IL and emerges at M.

A properly chosen lateral movement of the central housing is therefore sumcient to bring the optical axis into parallelism with the mechanical am's.

I have also discovered that this alignment can be accomplished by my novel method of rotating the central housing about two axes perpendicular to the piane'of the paper in Figure 11.

I have also discovered that this alignment can be accomplished by my novel method of rotating the central housing about any two axes not parallel to each other lying inthe plane of the paper in Figure 11.0r 12.

Properly chosen angles of rotation about two axes in the plane of the paper in Figure 12, said axes not to be parallel, will therefore be sumcient to bring the optical axis intoparallelism with the mechanical axis.

I It will now be clear from the above demonstrations that any movement of the central housing is either one or a combination of the above movements. f

The method described in the description of Figures 8, 9 and13 describes a novel method for causing the rotations of the last type. However, any suitable mechanism for causing one or more of the above motions may be employed. The central housing may be moved by a mechanism operated from within or from without the main housing. The former is preferable as the adjustinent can be made without danger of getting dust in the binocular or of altering the adjustment while closing up the binocular after the adjustment.

I claim:

1. In an optical system, a main housing, a system of lenses mounted in' said housing for producing an inverted image of a distant object, the rays from which are intercepted by said system and a system of a plurality of reflectors placed in the optical path for inverting the image, a central housing for rigidly supporting said reflectors,

aisassi comprising a plurality of screws rigidly secured to said central housing for the purpose of'adjusting said central housing together with the said reflectors rigidly attached thereto by rotating said central housing, about two axes thru said fixed point and lying in a plane perpendicular to the axis of the optical path, a plurality of screw heads fitting in openings in the main housing and screwing on to the ends of the aforementioned screws for the purpose of adjusting the'said'refiectors by moving the said screws in the direction of their length and means for maintaining said reflectors in positions fixed relative to each other and to the said central housing during said adjustment.

2. In an optical system, a main housing, a system of lenses mounted in said housing for pro= ducing an inverted image oi a distant object, the rays from which are intercepted by said system and a system of a plurality of reflectors placed in the optical path for inverting the ge, a central housing for rigidly supporting" said reflectors, means for holding a fixed point of said, a central housing rigid relative to the main housing,

axis of the optical path, a plurality of screw heads.

fitting in openings in the main housing and screwing on to the ends oi the afore-mentioned screws for the purpose of adjusting the said reflectors by moving the said screws in the direction of their length, and'ior the purpose of maintaining the said reflectors in a-fixed relative position to the mairfhousing after adjustment is completed by tightening said screw heads and keeping the said screws held by the said screw heads under tension and means for maintaining said reflectors in positions fixed relative to each other and to the 'said central housing after said adjustment. 

